import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution4 {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return bool布尔型
     */
    public boolean isCompleteTree (TreeNode root) {
        // write code here
        Queue<TreeNode> s = new LinkedList<>();
        if(root == null){
            return true;
        }
        s.offer(root);
        boolean flg = false;
        while(!s.isEmpty()){
            int size = s.size();
            for(int i = 0;i<size;i++){
                TreeNode cur = s.poll();
                if(cur == null){
                    flg = true;
                    break;
                }
                s.offer(cur.left);
                s.offer(cur.right);

            }
            if(flg){
                break;
            }
        }
        while(!s.isEmpty()){
            if(s.poll() != null){
                return false;
            }
        }
        return true;
    }
}